I picked one of these up the other day and figured, who would need instructions for a sub box. Well, this thing has an electrolytic section that's a little confusing. Does anyone have a clue how that section works? Or better yet a manual?

I took the time this morning to figure out the electrolytic section of my Sencore Handy 75. I have more detail if anyone wants it. But this will get you on the right path, if you just need to troubleshoot or use it.

First is slide slide switch that says “Push to Test” and “Surge Protector”. This switch is just an 8 terminal slide switch. The switch connects 2 pairs of terminals in the unlocked position and when slid over it connects other 2 pairs of terminals.

In the unlocked position, “Surge Protector”, it connects any selected capacitor on the rotary switch to common negative banana plug through a pair of 500 ohm resistors.

In the locked position, “Push to Test”, it connects the A+ banana plug to the top rotor plate of the rotary switch and the B+ banana plug to the bottom plate of the rotary switch.

The rotary switch connects 10 capacitors housed in 3 large multi capacitors to 10 of its terminals. The capacitances as best as I could read them were 125, 80, 40, 30, 25, 25, 10, 6, 2 and 2 mF. The top rotary plate (A+) connects up to 3 terminals/capacitors at a time in parallel. The bottom rotary plate (B+) connects 1 terminal/capacitor at a time.

So you have 2 capacitor values at each of the 10 switch positions. I’m guessing so you can substitute a filter capacitor in a radio. If you look at the knobs marked positions on the left the values are A/B and on the right they are B/A. Not sure why, but it must have to do with the combinations. My head already hurts, so I’ll leave that to you to figure out. In other words on the left side 20-25 is 20mF on A+ and 25mF on B+. On the right 80-100 is 80mF on B+ and 100mF on A+.

I found my 3 multi caps all very leaky. I also had to take my slide switch apart to clean the contacts and reverse one of the little contact slider things. One end was toasted and it wasn’t making continuity from the A+ to the rotary switch. I guess it needed a bit more surge protection.

I spent a long time just trying to find a manual and couldn’t. I hope this helps anyone with one of these boxes.

Having used a similar box many years ago when I was in the TV servicing biz, I can tell you how they are supposed to work from a user standpoint. You can, I am sure, take it from there.

First, in order to sub for a capacitor in a TV set or radio, you have to know (or have some idea) of the value of that cap. Once you know the value, you rotate the selector switch to a position where the cap in the set falls between the two numbers. In other words, each position of the rotary switch describes a range of values that can be substituted for in that position. It does not necessarily relate to the cap in the test box, which is probably roughly in the center of that range.

You then connect the leads to the set. It is assumed that the TV set or radio is ON and POWERED when you do this. The surge protect position of the slide switch places resistance in series with the capacitor in the box. This allows you to connect the test leads to a live circuit with a minimum of sparks. Once you have the leads connected, you can then move the slide switch to the "Test" position (usually spring loaded to return to the "surge protect" position). "Test" removes the series resistance and allows the capacitor in the box to be directly connected in parallel with the cap in the set. The TV set or radio is then observed to see if the problem has gone away. If so, the switch is returned to surge protect and the test leads disconnected. The cap that you just bridged is the culprit. If there is no improvement, the test leads are then moved to the next cap and the process is repeated.

As they are fairly old units, I would suggest replacing the electrolytics with fresh ones, the fixed caps, and check all the resistors for tolerances.

I have had to rebuild most of my sub boxes because the majority of the caps & resistors have gone out of tolerance. I became so irritated at all of the faults in them, I simply ordered a huge mass of all new caps and flame retardant resistors, and replaced the power resistors. Now I can be sure they are good. I must have 8-10 r/c sub boxes around here, plus the diode / rectifier sub boxes. Clean all the switches also, and lube the shafts.

Likely the selenium rectifier has failed also from age.

_________________FrankBWB7ELC"The average family has 2.5 children. Where is the other .5 child?"